This invention relates to sealing mechanisms for the shaft of a rotary pump, and more particularly to pumps having rotatable expellers.
Centrifugal pumps typically include some type of sealing arrangement at the shaft end of the pump. It is common, for example, to install packing in a stuffing box positioned about the shaft and to flush the packing with a supply of water or other liquid at higher pressure than the circulating pump pressure. Mechanical seals about the pump shaft also are often utilized.
To reduce the loading on the seals, pump impellers often include pump-out vanes on their rear surfaces and, in addition, a separate rotatable expeller is sometimes included to assist in reducing the pressure at the seals. The expeller commonly is smaller than the impeller and is affixed to and rotates at the same angular velocity as the pump shaft. Thus, the expellers do not create a sufficient head to overcome the head generated by the impeller.
Exemplary of such pumps is that shown in U.S. Pat. No. 3,213,798 which discloses a pump having an impeller mounted on the end of a shaft and floating ring type seals surrounding the shaft. A flushing fluid is injected into a passage adjacent the seals and an auxiliary impeller is mounted on and rotates directly with the shaft. Similar pump arrangements are shown in U.S. Pat. No. 3,429,268 which discloses a pump including a subsidiary impeller affixed through an inducer to rotate directly with the pump shaft; U.S. Pat. No. 2,127,865 which discloses a pump having radial vanes on the front and rear exterior surfaces of the primary impeller as well as a flange fixed to the pump shaft having moving vanes which cooperate with fixed vanes to prevent an inflow of air to the shaft; and, U.S. Pat. No. 1,932,214 which discloses a pump with two impellers mounted directly onto a shaft.
It is desirable to provide a pump arrangement which reduces the shaft seal loading and which overcomes or alleviates the head generated by the primary impeller contributing to fluid leakage. It is further desirable to reduce the head on the stuffing box or mechanical seals, or to reduce the need for these seals.